APPLICATION OF A MULTISTYLUS RECORDER TO THE ENERGY DISPERSIVE ANALYSIS OF PAINT FLAKES IN THE SCANNING ELECTRON MICROSCOPE

• NCJ Number: 47271
• Journal: Journal of Forensic Sciences Volume: 23 Issue: 2 Dated: (APRIL 1978) Pages: 274-282
• Author(s): R H MEINHOLD; R M SHARP
• Date Published: 1978
• Length: 9 pages
• Corporate Author: American Soc for Testing and Materials
• Sale Source: Dept of Scientific and Industrial Research
• Publication Format: Article
• Publication Type: Report (Study/Research)
• Language: English
• Country: United States of America

Annotation

TO EXAMINE THE DISCRIMINATIVE ABILITY AND REPRODUCIBILITY OF AN ENERGY DISPERSIVE X-RAY ANALYSIS TECHNIQUE USING A MULTISTYLUS CHART RECORDER TO PROVIDE A COMPOSITIONAL PROFILE, 20 AUTOMOBILE PAINT CHIPS WERE ANALYZED.

Abstract

PAINT FLAKES FOR ANALYSIS WERE TAKEN FROM FOUR LOCATIONS ON A WHITE VEHICLE AND FROM 15 DIFFERENT LIGHT BLUE VEHICLES. FLAKES WERE MOUNTED ON GRAPHITE BLOCKS AND COATED WITH A THIN CONDUCTING LAYER OF CARBON. FLAKES WERE MOUNTED TO SHOW A FRESHLY CUT EDGE AND PRIMER AND TOP COAT SURFACES. A SCANNING ELECTRON MICROSCOPE FITTED WITH AN ENERGY DISPERSIVE X-RAY ANALYZER WAS OPERATED WITH AN ACCELERATING VOLTAGE OF 25 KV AND A BEAM CURRENT OF 10 A TO THE -9TH POWER TO GIVE A COUNT RATE ON THE ORDER OF 1,000 COUNTS PER SECOND. AN AUCKLAND NUCLEAR ACCESSORY COMPANY MODEL 910 MULTISTYLUS CHART RECORDER WITH 128 WRITING CHANNELS WAS UTILIZED. THE CHART DRIVE, SYNCHRONIZED WITH THE SCANNING ELECTRON BEAM, PRODUCES A COMPOSITIONAL PROFILE IN WHICH THE ENERGY INTENSITY OF THE X-RAYS GENERATED ARE RECORDED AS A FUNCTION OF THE POSITION ON THE SPECIMEN. ANALYSIS OF FOUR FLAKES FROM THE SAME VEHICLE, ALTHOUGH OF VARYING THICKNESS, EASILY DEMONSTRATED THAT ALL FOUR FLAKES WERE FROM THE SAME CAR. AN ADDITIONAL ANALYSIS OF THE 15 LIGHT BLUE FLAKES ALSO ALLOWED EASY DISCRIMINATION OF ALL 15 SAMPLES. SAMPLES WITH PRIMER LAYERS ARE MOST SIMPLY AND RAPIDLY DISTINGUISHABLE. THE MULTISTYLUS RECORDER IS ABLE TO GIVE REPRODUCIBLE, REPRESENTATIVE SPECTRA AND LOCATE AND ANALYZE IMPURITIES. A FURTHER ANALYSIS OF 60 LIQUID TOPCOAT PAINTS USED BY 5 NEW ZEALAND ASSEMBLY PLANTS IN 1975 IDENTIFIED 4 MAIN GROUPS DISTINGUISHED BY THE MAJOR ELEMENTS PRESENT. THESE GROUPS MAY BE FURTHER SUBDIVIDED ON THE BASIS OF THE AMOUNT AND TYPE OF OTHER ELEMENTS PRESENT. IN GENERAL THE ENERGY DISPERSIVE X-RAY TECHNIQUE IS MOST USEFUL IN DISCRIMINATING AMONG GREEN, RED, YELLOW, AND BROWN. BLUES, PASTELS, AND WHITES ARE LESS READILY DISTINGUISHABLE. THIS METHOD PROVIDED A RAPID AND NONDESTRUCTIVE METHOD FOR IDENTIFYING THE MAIN ELEMENTS IN PIGMENTS, FILLERS, AND IMPURITIES IN PAINT AND IS PARTICULARLY USEFUL IN THE ANALYSIS OF SMALL SPECKS OR SMEARS WHERE CONVENTIONAL ANALYSES ARE NOT POSSIBLE AND IN THE ANALYSIS OF FLAKES WITH ONLY A FEW LAYERS. A LIST OF REFERENCES IS PROVIDED. (JAP)